1. Field of the Invention
The present invention relates to an apparatus and method for reproducing a 2- or 3-dimensional image from a hologram or a holographic stereogram on which two- or three-dimensional image data is recorded.
2. Description of the Related Art
A holographic stereogram is prepared by recording a number of rectangular or dot-shaped element holograms on one hologram-recording medium. The element holograms are original images that have been obtained by photographing an object, sequentially from different points of observation.
A holographic stereogram containing parallax data concerning only the horizontal direction, for example, is prepared as is illustrated in FIG. 1. First, an object 100 is photographed from different observation points that lie in the same horizontal plane. A number of original images 101a–101e of the object 100 are thereby obtained. Then, the original images 101a–101e, which are rectangular element holograms, are sequentially recorded on a hologram-recording medium 102.
The holographic stereogram records image data representing rectangular element holograms that have been obtained by photographing an object, sequentially from different observation points that lie in the same horizontal plane. When an observer looks at the holographic stereogram, the two 2-dimensional images his left eye and right eye receive, respectively, are different a little. The observer therefore perceives parallax and sees a 3-dimensional image.
An ordinary hologram is spaced from an illumination light source for reproducing a 3-dimensional image. A large space is required to reproduce the 3-dimensional image. To reproduce the 3-dimensional image in optimal conditions, the hologram and the light source need to have a particular positional relationship. This holds true of a holographic stereogram that consists of a plurality of element holograms.
If the hologram and the illumination light source are combined, no space is required for illumination. This helps to reduce the size of the apparatus for reproducing 3-dimensional images. In addition, a 3-dimensional image can always be reproduced in the best possible conditions because the hologram and the illumination light source have a fixed positional relation. A 3-dimensional image may be reproduced in such conditions from a so-called “edge-lit hologram.” A recording medium bonded to a transparent light-introducing block is used to reproduce a 3-dimensional image from an edge-lit hologram.
A transmitting hologram of edge-lit type, from which a 3-dimensional image can be reproduced, is prepared as is illustrated in FIG. 2. To be more specific, a hologram-recording medium 111 is bonded to one surface 110a of a transparent light-introducing block 110. The light-introducing block 110 is made of transparent material such as glass or plastic and has an appropriate thickness. In most cases, the medium 111 is bonded with index-matching liquid (not shown) to the light-introducing block 110. This prevents total reflection at the surface 110a of the block 110. Body light 114 from an object 113 is applied from the opposing surface 110b of the light-introducing block 110 to the hologram-recording medium 111. Reference light 115 is simultaneously applied from one end 110c of the block 110 to hologram-recording medium 111. A transmitting hologram of edge-lit type is thereby prepared.
To reproduce an image from the transmitting hologram of edge-lit type, thus prepared, the hologram-recording medium is bonded to a light-introducing block made of, for example, glass. More precisely, as shown in FIG. 3, a hologram 121 is bonded with index-matching liquid (not shown) to one surface 120a of a light-introducing block 120. Image-reproducing light 123 is applied from one end 120b of the block 120 to the hologram 121. The hologram 121 diffracts the light passing through it. The light 124 diffracted forms a reproduced image 125, which is observed by an observer 126.
As shown in FIG. 3, the image-reproducing light 123 is incident on the one end 120b of the block 120 at angle of 60°. Since the light 123 is thus applied to the hologram 121 through the light-introducing block 120, it is possible to prevent surface reflection at the interface between the hologram 121 and air. The larger the angle of incidence, the more readily the surface reflection can be prevented. In view of this it is considered that a compact apparatus can reproduce an image from the edge-lit hologram.
The hologram 121 and the light-introducing block 120 are bonded as shown in FIG. 3. The resultant unit is inevitably large, which is inconvenient in view of transportation and storage.
As pointed out above, the image-reproducing light 123 is incident on the one end 120b of the block 120 at angle of 60°. The hologram 121 may have a length L of 30 mm and the one surface 120a of the block 120 may have a length that is at least nearly equal to the length L. In this case, the light-introducing block 120 needs to be at least 17.3 m thick.
A number of edge-lit holograms are therefore inconvenient in view of transportation and storage. This is because, each edge-lit hologram is bonded to a light-introducing block that is 17.3 mm thick. That is, each edge-lit hologram must be transported and stored, together with such a long block.